ER9

i have three leopard danios iv'e had for a couple months now. the runt of the three was always the smallest. this fish has been extremely healthy and active up until a couple days ago when it just started hovering in one spot on the bottom. this danio never really grew much at all and the others are twice its size even though it always appeared very healthy. now it can barely swim up off the bottom of the tank. it has no visible signs of damage or illness at all. appearance....other than looking a little wasted away (thin) it looks fine. every other fish in the tank is acting normal and healthy. i'm guessing for whatever reason it just cant survive. maybe genetic problem etc....who knows. is this common in fish?

FishKing

The most logical explanation is it is being picked on by the larger danios to a point of harrassment. It is probably very exuasted from running.

ER9

i would agree with you except for the fact that half of the chasing was initiated by this little guy. i guess that is possible. i'm really puzzled by it and trying to figure out what else it could be. if it is some parasite or disease i want to try and catch it quickly and treat the tank before it spreads. confusing thing is the lack of visible illness on its body. over the past couple days the fish got very lethargic and would hide and hover on the bottom of the tank in one place. not eating of course. there's no bloating, no discolorations, only clamped fins. when it tries to swim it starts to turn upside down but recovers to the bottom. i'm thinking possibly dropsy but the lack of physical conditions make me wonder. i'd love to figure this out quickly if its still possible its a curable illness.

COBettaCouple

It sounds like internal parasites.